Improved rocket nozzle designs for vehicles with nozzles embedded in or protruding from surfaces remote from the desired thrust axis. The nozzle configurations are for rocket vehicles where the nozzles are not located at the optimal thrust axis of the vehicle. Two examples include nozzles located on the forward end of the vehicle (also called tractor nozzles) and attitude control nozzles located on the periphery of the vehicle. More particularly, the disclosed nozzle shapes enhance the axial thrusts and/or maneuver torques on the vehicle. These unconventional nozzle shapes improve vehicle performance.
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1. A vehicle, comprising;
a payload;
tractor rocket motors that are not installed at the base of the vehicle effective to generate thrust along a direction of flight of said vehicle;
each tractor rocket motor having a nozzle at a forward end of the vehicle protruding from an exterior wall and angularly disposed towards said base with an aft surface of said tractor rocket motor adjacent to said exterior wall of said vehicle and an opposing fore surface of said tractor rocket motor radially outward of said aft surface, said aft surface extending toward said base for a lesser distance than an opposing fore surface; and
said tractor rocket motors having a converging portion adjacent a source of subsonic propellant gas, a throat effective to accelerate said propellant gas to supersonic, said nozzle shaped to turn said gas through an angle by means of a plurality of Mach waves extending from an end of said aft surface to said fore surface.
2. The vehicle of
3. The vehicle of
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1. Field
Disclosed are nozzle configurations for rocket vehicles where the nozzles are not located at the optimal thrust axis of the vehicle. Two examples include nozzles located on the forward end of the vehicle (also called tractor nozzles) and attitude control nozzles located on the periphery of the vehicle. More particularly, the disclosed nozzle shapes enhance the axial thrusts and/or maneuver torques on the vehicle.
2. Description of the Related Art
In conventional rocket nozzle design, the flow and pressure in the nozzle is evaluated as a simple function of the local area to the throat area.
A is local flow area measured in square inches;
At is the sonic throat area measured in square inches;
Pc is the chamber total pressure measured in pounds per square inch;
P is local flow pressure measured in pounds per square inch; and
γ is specific heat ratio (unit-less).
Even this calculation has its limits in that the pressure, p, is the average at a station and the wall pressure may be more or less than the average p, a function of Pc & (A/At). This technique has been successfully employed to design axisymmetric nozzles following simple rules. Gas flows into the nozzle 10 at subsonic speed and through a converging portion 12 that terminates at throat 14. The gas then flows at supersonic speed through diverging portion 15 and through exit 16. The supersonic flow in the nozzle 10 responds to changes in the nozzle wall contour 17 through expansion or shock waves. These waves will travel from their origin across the nozzle 10 to the opposite side where they reflect and cross back and forth as the flow accelerates from the throat 14 to the exit 16. These waves are called characteristics or Mach waves and in the days before Computational Fluid Dynamics (CFD), were used to design and analyze the flow in a nozzle 10.
In a more general case, the wall contour 17 is not uniform as in this example and the pressure acting on the wall is affected directly by changes in wall angle and waves from the opposite side of the nozzle. Since the Mach waves move at the local speed of sound in the gas, they move away from the wall and are swept downstream by the supersonic flow. This means that wall angle changes affect the local pressure and the pressure on the opposite wall well downstream of the origin of that change. If, for example, the lower wall 26 was terminated at point A, the flow would expand out and downward causing another expansion fan to travel from A to B. Since B is beyond the exit of the nozzle the removal of this lower wall section will not change the pressures on the upper wall 28.
In most rocket propelled vehicles, one or more rocket nozzles are located at the aft end and aligned close to the vehicle axis to convert most of the thrust in flight direction. Some applications exist that preclude this aft location for nozzles. Exemplary tractor nozzle applications are the TOW missile and the escape motor for the Orion, Crew Exploration Vehicle. In another application, multiple rocket nozzles are arrayed around the vehicle for maneuvering. For both of these applications, using conventional nozzles can have a detrimental effect on vehicle performance.
Referring to
In the event that it becomes necessary to abort the mission prior to separation of the booster rocket 40 from the payload 34, abort motor 42 is ignited generating propellant gases that are expelled through nozzles 44. Nozzles 44 are angularly disposed in an aftward direction to the intended direction of flight of the vehicle and generate a thrust effective to separate the launch abort system and crew module 30 from the remainder of the vehicle 32. This propulsion system has a number of limitations. Hot propellant gases expelled by the nozzles 44 impact the abort motor 42 and crew module 36. These components must be designed to withstand the high temperatures that may be generated by impingement of the propellant gases. One approach, that was utilized on the Apollo program, is to cant the nozzles 44 at an extreme angle to expel the hot propellant gases sufficiently outward from the rocket components to avoid the most severe temperature increases. However, deviation of the nozzle direction from directly aftward causes a loss of thrust requiring abort motor 42 to be charged with additional propellant.
These limitations are illustrated in more detail in
Nozzles 44 project outward from exterior walls 48 of the abort motor 42 that arrayed around motor centerline 47. The abort motor 42 includes a propellant 49 that when ignited generates propellant gases. The propellant gases pass through nozzle throat 14 and are accelerated through divergent portion 15 of the nozzle. If the cant angle, α, of the nozzle is greater than the divergence angle, β, the wall 50 of the nozzle 44 generates a negative thrust due to the local nozzle pressures acting in a rearward direction. The opposite effect is seen on wall 53. Here the wall pressures 55 have a larger forward projected area and contribute more to the net thrust of the nozzle 44. However, with the conventional nozzle 44, the thrust is significantly less than an axially directed nozzle (due to the cosine loss from the previous paragraph).
Referring now to
Referring back to
The crew module 36 typically includes roll control nozzles 62 that control module roll while in orbit. As shown in
τ=F1*R1−F2*R2 (2)
Compensation for the counter torque requires more propellant to be consumed for a given maneuver than desired.
There remains a need for improved rocket nozzles, such as for a launch abort system, or the capsule attitude control system, that overcomes this loss of vehicle performance.
Disclosed are nozzle configurations for rocket vehicles where the nozzles are not located at the optimal thrust axis of the vehicle. Two examples include nozzles located on the forward end of the vehicle (also called tractor nozzles) and attitude control nozzles located on the periphery of the vehicle. More particularly, the disclosed nozzle shapes enhance the axial thrusts and/or maneuver torques on the vehicle
The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects and advantages of the invention will be apparent from the description and drawings, and from the claims.
Like reference numbers and designations in the various drawings indicated like elements.
The rocket plume 56 reacts to the change in nozzle 102 contour by turning and accelerating to a higher Mach number. This thrust increase is due to both the greater expansion and more axial jet angle, that is the exhaust flow is nearly axial in direction. By nearly axial, it is meant that axial jet angle has a deviation of less than 10° relative to the longitudinal axis 107 of the vehicle. By omitting the forward facing wall of the aft portion 104 of the nozzle, the flow is allowed to turn onto the exterior wall 48 of the motor case. This results in the flow remaining attached with little or no boundary layer separation keeping the heat flux similar to that within the nozzle 102. This thermal environment is then more benign and consistent over the flight speeds.
Returning to
As shown in
For vehicle maneuvering thrusters, the counter torque of prior art integrations exemplified by
τ′=F1*R1−F2′*R2′ (4)
F2′=P′*A2′<P*A2 (5)
P′ is much less than P and R2′ is less than R2 from the
In a second embodiment for a roll control nozzle 142, shown in
τ″=(F1*R1+F3*R3)−(F2*R2) (6)
and the contribution to desired torque is enhanced by (F3*R3) while the undesired counter-torque is reduced due to a small value for F2 as disclosed in the preceding embodiment.
In a third embodiment for a roll control nozzle 144, shown in
One or more embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, other embodiments are within the scope of the following claims.
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